1. Field of the Invention
Process for preparing p-t-butyl-.alpha.-methyldihydrocinnamaldelyde.
2. Prior Art
The compound p-t-butyl-.alpha.-methyldihydrocinnamaldehyde is one of the most important materials used in preparing fragrances. The usual method for preparing this compound is by the novel sequence of steps shown below. ##STR1##
A process that could be commercially attractive in theory is one that would allow the use of benzaldehyde, an economical and readily available compound, as a starting material. Such a process would require introducing the tertiary butyl group in the presence of an aldehyde group. The practical reality is, however, that a tertiary butyl group cannot be introduced in the presence of an aldehyde group because the aldehyde group cannot survive the reaction conditions necessary to carry out the tertiary butylation.
Some attempts have been made to circumvent this problem by converting the aldehyde group to the more stable alcohol group. The tertiary butylation is then performed on the alcohol and the alcohol is oxidized back to the aldehyde. (See, for example, the German Offenlegungsschrift DE No. 2,952,719 published July 16, 1981 and European patent publication No. 45,571 published Feb. 10, 1982). The disadvantage of such processes is the necessity of converting the alcohol back to the aldehyde. Such reactions are difficult to perform efficiently and economically. At high conversions, oxidation of the aldehyde to the acid occurs and this results in lower yields of the desired product. Attempts to minimize acid formation by stopping the reaction at lower conversions results in a mixture of starting alcohol and aldehyde, a mixture which is not easily separated by a simple distillation. The fact that neither of the references cited above provide any information with respect to yields in the oxidation step is consistent with the known difficulty with such conversions.
There is no prior art which teaches the tertiary butylation of an aldehyde derivative which can be easily and efficiently converted back to the aldehyde after the tertiary butyl group has been added. The requirements for such a process are not easily met. The aldehyde derivative should be sufficiently labile to be easily converted back to the aldehyde, but sufficiently stable to survive the reaction conditions during the tertiary butylation.